Captcha stands for Completely Automated Public Turing test to tell Computers and Humans Apart
The idea is that humans can read the letters, but computers cannot
Casey Chesnut, wrote a Captcha-breaking algorithm and demonstrated it by posting automated comments to nearly 100 blogs to demonstrate their vulnerability
Spammers have employed large teams of temporary staff to solve Captchas, effectively "rooms of people", usually in a third world country, sitting at a computer and solving Captchas.
OpenID, or Microsoft's CardSpace, may help
Instead of having many sites with poor
a few sites with strong verification procedures
"Ultimately Captchas are useless for spam because they're designed to tell you if someone is 'human' or not, but not whether something is spam or not. Just because something came from a real human being doesn't mean it isn't spam, which is why content-based solutions like Akismet are the only long-term solution to the spam problem."